1. Field of the Invention
The invention is related to computer memory control systems and specifically to systems for limiting access to a memory by a processor.
2. Description of the Prior Art
In a computer system, it is advantageous to provide password protection to prevent an unauthorized user from accessing information in the computer. To provide this protection, it is necessary to store the password in non-volatile memory. With the password in non-volatile memory, the password is retained while the system is turned off in order to limit use when the system is turned back on. It is also advantageous to protect the password information fromthe users of the system. The password holder may give another user access to the system by first typing his password and then giving the system to the other user. The password holder may still not want the other users to be able to find out the password or to change the password. This requires that the password be stored in non-volatile memory that is not accessible or changeable accept under firmware control. A typical personal computer contains a central processing unit (CPU) which executes user's programs and a system control processor (SCP), a peripheral processor that controls systems management. The SCP does not run application programs supplied by the user. The SCP only runs programs that are provided by the manufacturer in firmware. By running the password program on the SCP and not allowing the CPU to access the password, the system can prevent a careless or malicious user or users' application from discovering or changing the system password.